BACKGROUND: Congenital diaphragmatic hernia (CDH) still has a high mortality despite advanced assistance techniques. The aim of this study is to verify the validity of five respiratory and blood-gas-derived indices in defining presurgical stabilization: the oxygenation index (OI), the alveolar-arterial O2 gradient (A-aDO2), the arterial-alveolar O2 tension ratio (a/AO2), the arterial pH and the PaCO2.METHODS: The study involved 73 neonates with CDH where the accuracy of stabilization was assessed through the survival percentage and the contemporary behaviour of mean arterial pressure (MAP), ductal shunting, urine output and lactate levels. The trend of the indices was compared in two groups (stable/fit for surgery vs unstable/unfit for surgery) at five times (PICU admission, 6, 12, 24 hours after admission, assessment of clinical stabilization).RESULTS: Fifty-five neonates were defined stabilized on the basis of the indices and underwent surgery with a 100% survival rate; 18 patients died before surgery, having never achieved clinical stabilization. MAP, ductal shunting, urine output and lactate levels were normal in the stabilized patients and altered in the non stabilized. Of the five parameters considered, all three oxygenation-linked indices (OI, A-aDO2, a/AO2) are very powerful, whereas pH and PaCO2 appears valid but more tardive. Their progressive improvement (OI<10, A-aDO2<250 mmHg, a/AO2>0.50, PaCO2<55 mmHg, pH>7.35) defined presurgical stabilization, thus allowing CDH surgical correction.CONCLUSION: The study confirms the validity of these indices as a guide to the treatment of neonates with CDH, showing a good reliability in identifying presurgical stabilization.